Accurately knowing the humidity of ambient air surrounding an aircraft in flight is advantageous for many reasons. Icing conditions can be more accurately predicted based on ambient humidity. The crew can thus be alerted to turn on or off anti-icing systems. The humidity of ambient air also affects the operation of some military equipment. Accurately knowing the humidity aids the crews in carrying out a military flight mission.
Current methods of measuring ambient humidity are not suitable for measuring humidity of ambient air surrounding an aircraft in flight. One current method is to measure fiber expansion/contraction changes due to moisture absorption. Another current method is to measure the infrared energy attenuation in ambient air. Other methods are used by meteorologists, as is known in the art. Most of the current methods rely on the measuring devices being stationary. However, for an aircraft in flight, ambient air is passing by rapidly, often at supersonic speeds, thus preventing the use of conventional measuring devices. In addition, an aircraft in flight frequently changes altitude and rapidly passes through bands of air having radically different humidities from each other. The humidity of ambient air must be accurately known very quickly to be useful to the crew. Consequently, none of the current methods are sufficiently accurate or rapid for measuring ambient humidity for an aircraft while in flight.